1. Field of the Invention
The present invention relates to determining whether an information carrying bus used in an in-flight entertainment system is properly terminated.
2. Description of Related Art
Over the last few decades, commercial aircraft have become a necessary mode of travel for personal and business reasons. In order to improve passenger comfort, many commercial airlines now offer on-board telephony as well as in-flight entertainment such as video games, pay-per-view movies, hotel reservations services, and the like. Such amenities require supporting electronics distributed through the aircraft. Maintenance of the sophisticated electronics in in-flight entertainment systems (IFE) is a major concern of the airlines.
Quick servicing and maintenance of aircraft is important to the airline industry. The amount of time an aircraft spends on be ground represents lost flying time and lost profits. Diagnostic equipment which hooks up quickly to electronics aboard the aircraft and rapidly identifies problems is an important part of reducing aircraft servicing time. Designs which integrate the diagnostic electronics into the aircraft further reduce aircraft servicing time, thereby increasing aircraft flight time and airline industry profitability.
Diagnosis and maintenance of the IFE can be difficult because many of the entertainment system components, such as multiple seat electronic units (SEUs) are distributed throughout the passenger section of the aircraft. Each seat electronic unit (SEU) interfaces the IFE to several seats. Servicing SEUs scattered throughout the passenger section of an aircraft is a time consuming and tedious task. Thus there exists a need for a quick and efficient method of quickly diagnosing the entire IFE system.
One solution involves using an interconnect bus to link chains (i.e., daisy chain) of SEUs in a particular zone. In one implementation of a system sold by Sony Trans Com Inc. of Irvine, Calif., a common bus allows each SEU to communicate diagnostic information to a system manager unit (SMU) which oversees operation of the system. Diagnostic routines in the SEU and the SMU enable quick diagnosis of an entire daisy chained collection of SEUs greatly simplifying the diagnosis procedure.
After the SMU identifies a particular SEU as defective, the SEU can be rapidly replaced with a new SEU. In one embodiment designed by Sony Trans Com Inc., the SEUs throughout the aircraft have the same design and are thus interchangeable. The interchangeable characteristic of the SEU allows quick swapping and replacement of defective units and simplifies maintenance of the SEUs.
The rapid swapping of interchangeable SEUs sometimes results in an improper termination of the bus connecting the daisy chain of SEUs. In particular, the final seat electronics unit (FSEU) connected to the bus of daisy chained SEUs must include a terminating cap to properly terminate the bus. In one embodiment, the terminating cap includes a 100 ohm load resistor or other appropriate load which properly terminates the bus.
Failure to properly terminate the bus by putting a terminating cap on the last or final SEU (the FSEU) results in errors being introduced onto the bus. These errors result from uncontrolled reflections, primarily due to impedance mismatch. Such errors make communications unreliable. These errors may appear as various unpredictable error messages on the monitoring or diagnostic devices connected to the bus. Furthermore, a failure to properly terminate the bus results in electromagnetic emissions when the entertainment system is in use. Such electromagnetic emissions are particularly unsuitable for airborne applications where they may violate regulations promulgated by the Federal Aviation Administration.
In the rapid servicing of aircraft, airline personnel may easily forget to install the terminating cap as they swap SEUs. In light of the ease with which time pressured airline personnel may forget to install a terminating cap on a FSEU to terminate a bus, and the many problems associated with the failure to properly terminate the bus, a quick, efficient and inexpensive method of verifying the proper termination of a bus for a chain of SEUs is desirable. In particular, a system is needed which can quickly indicate to a monitoring unit when there is a failure to terminate a FSEU with an appropriate terminating cap.